Method of making electron tube



March 14, 1967 w. R. STUART 3,308,521

METHOD OF MAKING ELECTRON TUBE Filed Dec. 27, 1962 3 Sheets-Sheet 1 IN V EN TOR. WILLIAM R, STUART @Azm ATTORNEY MaI'Ch 14, 1967 w. R. STUART METHOD OF MAKING ELECTRON TUBE 3 Sheets-Sheet 2 Filed Dec. 27, 1962 6 v m 6 27 W V 5 9 m a m N w\ 1 m 2% av lim U l l l mw 1 U Ia VII fi l I IH 'N 5h p IN VEN TOR. WILLIAM R. STUART ATTORNEY March 14, 1967 A w. R. STUART 3,308,521

METHOD OF MAKING ELECTRON TUBE Filed Dec. 27, 1962 SSheecs-Sheet 3 INVENTOR. WILLIAM R. STUART ATTORNEY United States Patent C) 3,308,521 METHOD OF MAKING ELECTRON TUBE William R. Stuart, San Carlos, Calif., assignor, by mesne assignments, to Varian Associates, a corporation of California Filed Dec. 27, 1962, Ser. No. 247,718 Claims. (Cl. 2925.16)

This invention relates to electron tubes and more particularly to an improved tetrode of the type known in industry as the 4X150 series and described in the patent to Drieschman et al., No. 2,472,942, issued June 14, 1949.

The 4X150 type of tube construction has been widely used over the years. However, recent requirements have made it necessary for the tubes to be able to meet new specifications calling for ability to withstand extreme shock and vibration and also requiring improved accuracy in electrode alignment.

Accordingly, the object of this invention is to provide an improved method of making electron tubes such as the 4X150 type tube in a manner which will result in tubes having precise electrode alignment and having improved ability to withstand shock and vibration.

The problem has been to obtain the desired improvements without departing from the terminal arrangement and general internal and external configuration of the conventional 4X150 type tubes. The reason of course is that considerable time and money has been invested in the design and construction of equipment which uses the 4Xl50 tube type. The improved tube according to this invention is therefore designed to be usable in existing equipment.

The specific construction which provides the desired improvements will be hereinafter described in detail, and where possible comparison will be drawn to prior 4X150 type construction.

These and other objects and features of advantage will become apparent from a reading of the following detailed description wherein reference is made to the accompanying drawings in which:

FIGURE 1 is a cross sectional view on the centerline of an improved tube according to the invention;

FIGURE 2 is a bottom view of the tube of FIGURE 1;

FIGURE 3 is a view on line 3-3 of FIGURE 1 showing a stage of construction called the header assembly;

FIGURE 4 is a cross sectional view of the header assembly in a jig for assembling it;

FIGURE 5 is a top view of FIGURE 4 with the ceramic header disk and all parts above it removed;

FIGURE 6 is a side elevation of the header assembly from another angle with parts cut away and showing the cathode and cathode jig in position; and

FIGURE 7 is a view similar to FIGURE 6 but showing the control grid and control grid jig in position.

Referring in more detail to the drawings, an attempt will be made to describe first the construction which is either shown in the Drieschman et al. Patent No. 2,472,- 942 or utilized in improved versions thereof prior to this invention. The tube of FIGURE 1 comprises a heater coil 1, a cathode 2, a control grid 3, a screen grid 4 and an anode 5.

The envelope for the tube is formed in part by the inverted cup-shaped metal anode 5. The remainder of the envelope is formed by the metal ring 7, brazed to the bottom of the anode and to the top of a ceramic cylinder 8 which is metalized in conventional manner for this purpose; a metal sealing ring 9 and a metal shell 10 which are sealed together by a final braze or weld 11, with ring 9 being brazed to the bottom of ceramic cylinder 8 which is metalized for this purpose; and a ceramic header disk 12 which has an annular metalized area brazed to shell 10.

As regards terminals for the electrodes, the outer por- 3,308,521 Patented Mar. 14, 1967 "ice tion of the anode of course serves as its own terminal. The ring 9 and shell 10 can serve as the terminal for the screen grid 4. The remaining terminals are formed by pins sealed in the header disk 12. Eight small diameter pins 14-21 are arranged in a circular array around a large diameter center pin 22. Although eight small pins are employed only six of them are required as terminals. In the construction shown, pins 14, 16, 18 and 20 serve as cathode terminals and pins 17 and 21 serve as heater terminals. In the preferred design, pin 19 serves as the screen grid terminal by metalizing a conductive strip 23 on the bottom of header 12 from the pin to the metal shell 10. The center pin 22 is the control grid terminal. The center pin is sealed in the header by metalizing the wall of the aperture in the header and brazing the pin thereto. In the case of the small pins the apertures in the header are not metalized but instead an annular area is metalized on the bottom of the header around each pin. A copper washer 24 is brazed to the metalizing and the pin, and a Kovar Washer 25 is brazed to the copper washer and to the pin.

The anode structure is completed by brazing on conventional metal cooling fins 27 and a two-piece metal cover 28 over the pinched-0E exhaust tubulation 29. The anode structure is preferably impact formed so that the tubulation 29 can be made as an integral part thereof.

The cathode 2 is an inverted cup-shaped metal can having an electron emissive coating on its outer surface. The heater 1 is brazed or spot welded at its opposite ends to two metal posts 31 and 32. A ceramic disk 33 is apertured to receive posts 31 and 32 and serves as a heat barrier and shield. The disk is attached to the posts by two small wires 34 which pass through apertures in the disk and are spot welded at each end to the posts. A conventional getter strip 35 is spot welded to post 32. The grids 3 and 4 are conventional cage-type wire structures, each having an inverted cup-shaped configuration. It will be noted that the screen and control grids and the cathode all have metal end portions 36, 37 and 38, respectively.

Control grid 3 is supported by means of a metal ring 40 attached to the bottom thereof and having two downwardly extending projections 41 on its diametrically opposlte sides (only one such projection being visible in FIG- URE 1). A supporting yoke structure is formed by two U-shaped rods 42 brazed at their ends to the projections 41 and at their center in a slot in the top of the center pin 22. Although the construction thus far described is not exactly the same in all respects as prior structures, it does not involve features which are claimed per se as new herein.

The improved features according to the invention will now be described. Starting with the cathode support, it will be noted that the cathode support ring 44 has four channel-shaped legs 45. It is important that the channel construction extends along the sides of the pins 14, 16, 18 and 20. The reasons why this construction is important are that is makes it possible to braze the legs 45 to the pins and makes a much more rigid structure. In the past, legs similar to legs 45 have been spot welded to the pins. This not only involves four spot welds contrasted to a single braze step but more importantly often results in distortion of the legs. Although in the past legs similar to legs 45 have been ribbed along the free portion thereof for rigidity, they were flat where attached to the pins. It has been found that extending the channel shape along the sides of the pins solves the rigidity problem whereas the prior construction does not. In addition, the new channel construction simplifies assembly by providing a socket in the end of each leg which receives the end of a pin so that the problem of holding the legs oriented in place on the pins during attachment is avoided. Also the new construction provides a cavity in which to place the brazing material which joins the legs and pins.

At this point it is desirable to recall that the general purpose of the invention is to provide an improved construction which is physically more rugged, has more accurate electrode alignment and yet is simple to manufacture. Many of the novel features of the invention are so designed as to combine all three of the described objectives. Thus, the shape of the cathode support legs accomplishes improved rigidity, improved accuracy in making the cathode precisely coaxial with the tube, and improved assembly technique.

Continuing with description of the cathode supporting means, a very thin metal heat darn 46 is attached to the lower end of the cathode can. The lower end of the heat dam is spot welded to the outer surface of the support ring 44. In the past the construction and assembly technique was such that the heat darn was attached to the inside of the support ring. As a result of this change the weld is made through the very thin metal heat dam and therefore can be a very light weld which does not distort the members, thus insuring accurate positioning of the cathode.

Although the improvements already described result in substantial improvement in the alignment, rigidity, and assembly technique for the cathode, the rigidity aspect is even further improved by a construction which forms the cathode and heater into a composite assembly. The heater posts 31 and 32 are brazed at their lower ends in legs 47 and 48. As in the case of the cathode support legs, and for the same reasons, the heater legs are channelshaped including the portion which extends over and is brazed to the terminal pins 17 and 21, respectively. One important aspect of the cathode-heater combination is the use of a ceramic rigidifying disk 50 which is metalized on its outer periphery and brazed to the cathode support ring 44. The disk 50 is apertured to receive heater posts 31 and 32, and the walls of the apertures are metalized and brazed to the posts. Thus it will be appreciated that not only are the cathode and heater supported individually in rigid manner by channel-shaped legs brazed in place but these two structures are reinforced by the interconnection through ceramic disk 50. As a result the heater and cathode are firmly locked against movement relative to each other or movement relative to the header disk 12.

The lower end of the screen grid 4 is attached to a metal cone 52 mounted on a metal support ring 53. The cone is attached to ring 53 by screws 54 (preferably three) which abut the cone and are received in threaded apertures in the ring. Ring 53 has a three-part shape comprising a cylindrical side portion 55 brazed to shell 10, a fiat cone-supporting portion 56, and a downturned centering flange portion 57 at its inner periphery. The importance of the centering function of the ring 53 will become apparent when the assembly technique for the tube is hereinafter described. However, it will be noted at this point that the apertures for screws 54 are so positioned that when the screws are inserted in members 52 and 53, member 52 is centered with respect to flange 57.

Another feature of importance is the centering pin 60. Pin 66 is made of ceramic and its periphery is metalized where it passes through the screen and control grid ends 36 and 37 and is brazed to these ends. The apertures in the cathode and grids are centered in these electrodes and have a snug fit with the pin 60. In addition the pin has a large disk portion 61 between the cathode and control grid to reduce the capacitance between these electrodes. It will be understood that pin 60 contributes materially to precise alignment of the cathode and grids and to the rigid interconnection of these electrodes.

The improved construction thus far described makes it possible to assemble the electrodes in a simple and accurate manner. In the past it was necessary to assemble the tube in a much more complicated and tedious manner. For example, two separate spot welds were required to attach the heater legs 47, 48 to the heater pins, and four separate spot welds were required for the cathode legs 45. Then as a result of the distortion caused by the welds, it was necessary for highly skilled labor to bend the legs with tweezers to align the heater and cathode visually with the tube axis. The control grid was mounted on yokes 42 and projections 41 were bents where necessary to make the control grid approach concentricity with the cathode. Since the results of this hand alignment were very often imperfect, it became necessary to hand pick a screen grid which, when mounted on ring 53, would have distortions matching those of the cathode and control grid, or it was necessary to rebend the cathode and control grid to match the mounted screen grid.

The improved construction makes it possible to assemble in a jig and connect in a single braze all the following parts, called the header assembly 62 as indicated in FIGURES 3 and 4: shell 10; pins 14-22; washers 24 and 25; heater posts 31 and 32; control grid yokes 42; cathode support ring 44 with legs 45 fitted over their respective terminal pins; legs 47 and 48 fitted over their respective pins; ceramic disks 33 and 50; and the centering and screen support ring 53. All of the previously described brazes involving these various parts are made in this single brazing operation except that it has been found convenient to form the heater-post assembly in a preceding operation. More specifically posts 31 and 32, ceramic disk 33, wires 34, ceramic disk 50, and legs 47 and 48 are preferably prejoined with higher temperature bonds. The centering flange 57 provides a relatively large inner surface which can be formed to close tolerance, retain such size, and provide a relatively large reference surface for centering the tops of the cathode and control grid when they are attached to the header assembly, as will be hereinafter described.

FIGURES 4 and 5 show the jig for performing the assembly technique described in the preceding paragraph. As shown in FIGURE 4 the header assembly parts are mounted upside down in the jig. More specifically, the jig comprises a bottom portion having a base 66 with a cylindrical projection 67, and an inner sleeve 68 held by pins 69. The upper portion of the jig comprises a weight and centering ring 71, a pin holding ring 72 and a weight 73. FIGURE 5 is a top view of FIGURE 4 with the header disk 12 and everything above it removed.

The jig centers, rotationally orients, and vertically positions the parts as follows. A bore 74 in base 66 centers the heater post 31. A bore 75 in sleeve 68 centers the cathode support ring 44. The rim 76 on projection 67 centers the centering flange 57. The upper edge of projection 67 vertically positions the legs 45 and 47, 48. The fact that legs 45 are rigid means that when they are positioned on projection 67, the plane of the cathode support ring is exactly normal to the tube axis. A shoulder 77 on projection 67 vertically positions the screen support ring 53. Upwardly extending projections 78, 79, 80 and 81 vertically position the ceramic disk 12, and rotationally position the legs 45 and 47, 48. The U-shaped rods 42 are rotationally and vertically positioned by bores 82 in the upper end of sleeve 68. The parts are loaded into the jig in the following order: screen grid ring 53, cathode support ring 44; heater assembly including legs 47 and 48-; U-shaped rods 42; ceramic disk 12; pins 14-22; washers 24 and 25, and shell 10. Brazing material preferably in paste form, is placed where necessary during assembly of the parts in the jig, and the loaded jig is passed through a brazing furnace to provide the completed header assembly 62. It should now be clear that when the header assembly is brazed together in an accurate jig, the cathode support ring 44 is exactly centered and aligned with the centering flange 57.

Having thus fabricated the header assembly to accomplish the basic centering with assurance, the cathode structure may be lowered into place with the heat dam 46 centering itself around the cathode support ring 44 to accomplish perfect centering of the bottom of the cathode structure. The centering flange 57 is employed to accomplish perfect centering of the top of the cathode by means of a jig 84 as shown in FIGURE 6. The jig comprises a cylindrical wall portion 85 having four equally spaced legs 86 projecting therefrom, only two such legs being shown in the drawing. Each leg has an accurately formed centering lip 87, which engages the centering flange 57, and an abutment surface 88 which rests on the flat portion 56 of ring 53. Mounted in the cylindrical portion 85 is a block 89 which engages the top of the cathode and insures that the cathode is pushed down to the proper elevation. Block 89 is preferably magnetic material to facilitate loading the cathode in the jig. A centering pin 90 is mounted in the jig in centered relation to centering lips 87 and engages the walls of the aperture in the top of the cathode can 2, the same aperture which later receives the ceramic pin 60. After the cathode, jig and header assembly are positioned as shown in FIGURE 6, the heat dam 46 is spot welded to the cathode support ring 44. The legs 86 are of course widely enough spaced to permit insertion of the welding tool. The jig is then removed with assurance that the cathode is perfectly centered and aligned top and bottom.

After the cathode is mounted, the control grid is positioned by a jig 84 (FIGURE 7) similar to jig 84. The main diiference in the jigs is that the control grid jig has an aperture 91 in place of pin 90 in the cathode jig. The reason is that when the control grid is mounted the ceramic pin 60 is prebrazed therein, and the pin 60 is simply received in the aperture 91 in the control grid jig. The remaining portions of the jig 84' are given primed reference numbers to designate parts similar to the parts designated with unprimed numbers in jig 84. In jig 84 there are preferably only two legs 86', each being somewhat wider than legs 86. Legs 86' provide two openings for placing brazing material at the joint between yoke rods 42 and the control grid projection 41. It will be noted that the aperture 91 is oversized with respect to pin 60 and that the bore in the upper end of the cylindrical wall 85' is oversized with respect to the end 37 on the control grid. Thus, the top of the control grid is centered by reception of pin 60 in the aperture in the top of the cathode cam, and the bottom is centered by engagement between the jig wall 85' and the control grid ring 40. Projections 41 on the control grid ring are then brazed to yokes 42 while the jig is in place and then jig 84 is removed. The remaining parts of the tube are then assembled in conventional manner except that pin 60 automatically centers the top of the screen grid 4.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is as follows:

1. A method of making an electron tube of the type having a header assembly comprising a ceramic header disk, a metal shell joined to said header, a metal screen grid support joined to said shell and having a centering flange at its inner periphery, metal terminal pins extending through and joined to said header disk, two heater posts having metal legs thereon joined to some of said pins, a ceramic rigidifying disk carried by said posts, a metal cathode support ring joined to the periphery of said rigidifying disk and having legs joined to others of said pins, and a U-shaped metal yoke joined to another one of said pins; said method comprising the steps of first connecting all of said joined parts by a single braze step while holding said cathode support ring coaxial With said centering flange; next mounting an inverted cup-shaped cathode structure with the bottom of the structure centered by engagement with the periphery of said cathode support ring and the top of said cathode structure being centered by engagement between the wall of a center aperture in the top of said cathode structure and a pin in a cathode jig, said jig being self-centered wit-h respect to said cathode support ring by engagement with said centering flange; next spot welding said cathode structure to the outside of said cathode support ring and then removing said cathode jig; next mounting an inverted cylindrical cage-shaped control grid over said cathode, the top of said grid having a centering pin pro-brazed therein, said grid being centered at its top by engagement between said centering pin and the wall of said aperture in the top of said cathode, and the bottom of said grid being centered by engagement with a jig which is centered by engagement with said centering flange; and then brazing said control grid to said yoke and thereafter removing said control grid jig.

2. A method of making an electron tube of the type having a header assembly comprising a ceramic header disk, a metal shell joined to said header, a metal screen grid support ring joined to said shell and having a circular centering opening at its inner periphery, metal terminal pins extending through and joined to said header, a metal cathode support ring having legs joined to some of said pins, and a U-shaped metal yoke joined to another one of said pins; said method comprising the steps of first connecting all of said joined parts by braze connections while holding said cathode support ring coaxial with said centering opening, next mounting an inverted cupshaped cathode structure with the bottom of the structure centered by engagement with said cathode support ring, and the top of said cathode structure being centered by engagement with the upper end portion in a cathode jig, said jig being self-centered with respect to said cathode support ring by engagement with said centering opening; and then bonding said cathode structure to said cathode support ring and thereafter removing said cathode jig.

3. A method according to claim 2 further comprising the step of mounting an inverted cylindrical cage-shaped control grid over said cathode, the bottom of said control grid being centered by engagement with a jig which centers itself by engagement with said centering opening, and then bonding said control grid to said yoke and thereafter removing said control grid jig.

4. A method according to claim 3 further comprising centering the top of said control grid by engagement with a centering pin held centered with respect to said cathode.

5. A method according to claim 4 further comprising mounting an inverted cylindrical cage-shaped screen grid structure over said control grid with the top of said screen grid being centered by engagement with said centering pin, and thereafter attaching the bottom of said screen grid structure to said screen grid support ring in centered relation to said centering opening.

JOHN F. CAMPBELL, Primary Examiner.

WILLIAM I. BROOKS, Examiner. 

2. A METHOD OF MAKING AN ELECTRON TUBE OF THE TYPE HAVING A HEADER ASSEMBLY COMPRISING A CERAMIC HEADER DISK, A METAL SHELL JOINED TO SAID HEADER, A METAL SCREEN GRID SUPPORT RING JOINED TO SAID SHELL AND HAVING A CIRCULAR CENTERING OPENING AT ITS INNER PERIPHERY, METAL TERMINAL PINS EXTENDING THROUGH AND JOINED TO SAID HEADER, A METAL CATHODE SUPPORT RING HAVING LEGS JOINED TO SOME OF SAID PINS, AND A U-SHAPED METAL YOKE JOINED TO ANOTHER ONE OF SAID PINS; SAID METHOD COMPRISING THE STEPS OF FIRST CONNECTING ALL OF SAID JOINED PARTS BY BRAZE CONNECTIONS WHILE HOLDING SAID CATHODE SUPPORT RING COAXIAL WITH SAID CENTERING OPENING, NEXT MOUNTING AN INVERTED CUPSHAPED CATHODE STRUCTURE WITH THE BOTTOM OF THE STRUCTURE CENTERED BY ENGAGEMENT WITH SAID CATHODE SUPPORT RING, AND THE TOP OF SAID CATHODE STRUCTURE BEING CENTERED BY ENGAGEMENT WITH THE UPPER END PORTION IN A CATHODE JIG, SAID JIG BEING SELF-CENTERED WITH RESPECT TO SAID CATHODE SUPPORT RING BY ENGAGEMENT WITH SAID CENTERING OPENING; AND THEN BONDING SAID CATHODE STRUCTURE TO SAID CATHODE SUPPORT RING AND THEREAFTER REMOVING SAID CATHODE JIG. 